These are out-of-phase lattice vibrations in the plane of the thin sample, arising when neigh- bouring atoms in the lattice have different charge or mass. Until now, lattice vibrations were something electron microscopists have had to worry about only in terms of the sample damage that they induce, or when matching experimental images to simulations 7 . However, the main point of Krivanek and colleagues’ work is that optical phonons are key signatures of chemical bonds, particularly those involving light ele- ments such as hydrogen, as is well established by the techniques of infrared and Raman (opti- cal) spectroscopy. The implication is, there- fore, that STEM–EELS may provide a route for the direct mapping of chemical bonding, including that associated with light elements, at near-atomic resolution. This achievement would present tremendous benefits in a number of highly topical areas of research into new advanced materials and devices. The improvements in overall energy resolution of EELS will undoubtedly aid the study of the local spatial variation of energy bandgaps in semiconducting structures, and the identification of localized collective oscil- lation of electrons in ‘plasmonic’ structures for light capture. The ability to detect and map light elements, including hydrogen, could extend the existing capability of analytical electron micro- scopy to the study of organic materials such as polymers and pharmaceuticals, as well as energy-storage materials — if issues associated with electron-beam-induced damage can be addressed. Directly measuring phonons could potentially help to identify chemical reactions involving the surfaces of nanoscale hetero- geneous catalyst particles, and could aid the investigation of the transmission of lattice vibra- tions across micro- and nanostructural features, such as interfaces and defects in thermal and optical materials. As with the emergence of any new technique, many additional research areas may ultimately prove to be most fruitful. Existing theory suggests that electrons that have undergone phonon scattering would be scattered through large angles and the result- ing phonon signal would be spatially highly delocalized, preventing atomic-resolution analysis. However, Krivanek and colleagues present some initial findings which, together with recent theoretical predictions 8 , suggest that under appropriate conditions the phonon signal may be sufficiently localized for the study of vibrations at a spatial resolution better than that achieved by scanning probe tip-enhanced vibrational spectroscopies 9 . The authors observed an exponential delocalization of the phonon signal as an electron probe is moved away from the surface of a sample and into the surrounding vacuum. However, there seems to be a more localized component of the signal that peaks in intensity close to the surface itself, and the researchers discuss a possible experimen- tal geometry for signal collection that would ANIMAL BEHAVIOUR Incipient tradition in wild chimpanzees The adoption of a new form of tool use has been observed to spread along social-network pathways in a chimpanzee community. The finding offers the first direct evidence of cultural diffusion in these animals in the wild. enhance this more localized contribution. Furthermore, if the probe is inside the sample, it seems that the delocalization could be screened at the interface between two materials with different electrical properties. The authors also demonstrate a method for remotely exciting such phonons at a surface using the inherent delocalization of the signal; here, the beam is located in the vacuum close to the edge of a sample, potentially helping to mitigate electron-beam-induced damage of radiation-sensitive samples. These investiga- tions of the spatial resolution of the phonon signal represent a clear example of experiment leading theory in terms of the interpretation of the results, and is indicative of the new experi- mental landscape that this development in instrumentation unfolds. Undoubtedly, many more exciting experiments with this technol- ogy will follow, aided by the delivery, later in 2014, of a third-generation instrument to a shared user facility: the Engineering and Physical Sciences Research Council National Facility for Aberration-Corrected STEM, or SuperSTEM 10 , in Daresbury, UK. I look forward to the community charting this new frontier of research. ■ Rik Brydson is at the Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, UK. e-mail: [email protected] 1. Krivanek, O. L. et al. Nature 514, 209–212 (2014). 2. Krivanek, O. L. et al. Phil. Trans. R. Soc. A 367, 3683–3697 (2009). 3. Krivanek, O. L. et al. Microscopy 62, 3–21 (2013). 4. Bleloch, A. & Ramasse, Q. in Aberration-Corrected Analytical Transmission Electron Microscopy (ed. Brydson, R.) Ch. 4, 55–87 (Wiley, 2011). 5. Egerton, R. F. Electron Energy Loss Spectroscopy in the Electron Microscope 3rd edn (Springer, 2011). 6. Mahan, G. D. Condensed Matter in a Nutshell (Princeton Univ. Press, 2010). 7. Williams, D. B. & Carter, C. B. Transmission Electron Microscopy 2nd edn (Springer, 2009). 8. Dwyer, C. Phys. Rev. B 89, 054103 (2014). 9. Hermann, P. et al. Analyst 136, 1148–1152 (2011). 10.www.superstem.org ANDREW WHITEN S ocial learning — learning from others — is one of the fastest-expanding research fields in animal behaviour 1,2 . At the fundamental level of evolutionary biology, social learning provides a high-speed ‘second inheritance system’ that interacts with genetic inheritance to enrich behavioural evolution 2 . From a more anthropocentric perspective, ani- mal social learning casts light on the evolution- ary foundations of the cultural capacities that make our own species so successful. Studies of putative cultural variations in wild chim- panzees 2–4 , the primates with which (together with bonobos) humans last shared a common ancestor, have been particularly influential in our understanding of behavioural evolu- tion. But these observed regional behavioural differences have displayed little change, mak- ing it difficult to investigate the workings of social learning. Now, writing in PLoS Biology, Hobaiter et al. 5 describe a new form of tool use in the Sonso community of chimpanzees of the Budongo Forest in Uganda, and present a sta- tistical technique for tracing the social trans- mission of this innovation. Chimpanzees at Sonso fold wads of leaves in their mouths to fashion a ‘leaf sponge’ that they dip into tree holes to extract water to drink. In 2011, the researchers observed the dominant male of the group, Nick, creating a sponge of moss gathered from a tree trunk and using it to drink from a small flooded waterhole — a behaviour not previously recorded in the 20-year research programme at the site. He was watched by the dominant female, Nambi. Over the next six days of intensive and often competitive use of the waterhole (which the researchers suspect contained unusual densi- ties of minerals or other desirable content), Nambi and six other chimpanzees began to display the moss-sponging technique (Fig. 1a). More than 20 other individuals drank at the hole or in puddles around it, but either directly with their mouths or using leaf sponges rather than moss sponges. To establish whether this behavioural spread was due to social learning, the researchers developed a form of network-based diffusion analysis (NBDA). This statistical technique quantifies the extent to which the spread of a new behaviour is consistent with the prediction that it will follow the social network — a 178 | NATURE | VOL 514 | 9 OCTOBER 2014 NEWS & VIEWS RESEARCH © 2014 Macmillan Publishers Limited. All rights reserved